As we move increasingly towards market viable net-zero buildings with initiatives like ASHRAE Vision 2020 and the 2030 Challenge, we must reevaluate the role that typical building components play in a facility’s energy efficiency. ASHRAE 55 has highlighted the impact of elevated air speed on thermal comfort, and in recent years innovative designs have reestablished air movement as an integral part of occupant comfort and energy conservation. Furthermore, recent changes to Appendix G of ASHRAE 90.1 allow the inclusion of energy savings from using elevated air speed in energy simulations. When integrated into new building designs, air movement allows a reduction of air conditioning capacity and ductwork. In the winter, low speed air circulation redirects heated air trapped at the ceiling, resulting in significant energy savings. Project teams working on net-zero buildings have proven the effectiveness of incorporating air movement in building plans as part of an integrated design strategy.
Indoor environmental quality (IEQ) is a significant concern in today’s design and building, as we spend the majority of our time indoors. The U.S. Green Building Council’s Green Building and LEED Core Concepts notes, “…strategies that improve employee health and productivity over the long run can have a large return on investment.” To maximize occupant health and promote sustainable building practices, understanding IEQ and thermal comfort is of key importance when approaching a new building project or renovation.
Human thermal comfort, as defined by ASHRAE Standard 55-2010 Thermal Environmental Conditions for Human Occupancy, takes into account numerous environmental factors including temperature, thermal radiation, humidity and air speed, along with personal factors including activity level and clothing. A thermal environment acceptable to at least 80 percent of the occupants is considered acceptable per Standard 55.
Incorporating gentle air movement with high volume, low speed ceiling fans can provide significant energy savings and improve occupant comfort year round, allowing ASHRAE thermal comfort standards to be met with reduced or eliminated ductwork and air conditioning tonnage. Resulting in both front- and back-end savings and a reduction of energy consumption, air movement can also contribute to earning certain LEED credits. In fact, project teams working towards market viable net-zero buildings worldwide have proven the effectiveness of incorporating air movement in building plans as part of an integrated design strategy. Some examples include:
Oakland Unified School District
Oakland Unified School District’s downtown educational complex is designed to be a Collaborative for High Performance Schools (CHPS) Verified project, with a target of 59 points. Engineers had to find a way to meet ASHRAE 55-2010 Thermal Environmental Conditions for Human Occupancy requirements without traditional, energy-intensive air conditioning. A three-layer strategy for maintaining comfort conditions utilizes a nighttime cooling cycle, high thermal mass walls and elevated air speed.
Locust Trace High School
Situated on 82 acres of government-donated land on the outskirts of Lexington, Ky., Locust Trace High School offers an innovative campus designed to educate students for careers in equine and agriculture sciences. The net-zero facility includes clerestory windows for day lighting, solar tube illumination supplemented with high-efficiency lighting and renewable energy through photovoltaic panels. Inside, air circulation helps regulate indoor environmental quality and aids in the distribution of conditioned air, augmenting natural ventilation and a roof solar thermal system to maximize comfort and energy conservation.
- Primary factors affecting human thermal comfort and basics of ASHRAE Standard 55-2010 and the ASHRAE Thermal Comfort Tool.
- Use of elevated air speed for increased air distribution efficiency & energy savings within air conditioned spaces.
- Additional design benefits of minimizing ductwork, lower HVAC first cost, improved ventilation rates, and condensation reduction.
- Stratification & Destratification, and the significant energy saving potential from destratifying a large open space.